Gas safety means for use in hot blast stoves



June 19, 1962 B. SCHOLL GAS SAFETY MEANS FOR USE IN HOT BLAST STOVES 2Sheets-Sheet 1 Filed Nov. 18, 1958 AONFELOQ AVE- 1 ":4 u Juan INVENTOR.BERNHARD S CHOLL ATTORNEY June 19,

B.SCHOLL GAS SAFETY MEANS FOR USE IN HOT BLAST STOVES Filed Nov. 18,1958 2 Sheets-Sheet 2 u as 041* o O 0 A g 8 m if I'( '3 m k k. k. x o -o,o N Q Q W K w w E? g E g h. Q1 m m U) 3 a S *Q I 0 fig Q, E 5

INVENTOR. fie/Wfiard Jcfia/Z' United States Patent 3,039,522 GAS SAFETYMEANS FOR USE IN HOT BLAST STOVES Bernhard Scholl, Duren, Rhineland,Germany, assignor to Zimmermann & Jansen G.m.b.H., Duren, Rhineland,

Germany, a corporation of Germany Filed Nov. 18, 1958, Ser. No. 774,6904 Claims. (Cl. 158-123) The present invention relates to gas safetymeans for hot blast stoves.

During the heating of the hot-blast stove, gas and air are burned in thecombustion chamber. The gas and the air are separately fed to thehot-blast stove through the burner. A control element such as abutterfly valve or the like in the gas feed duct permits an appropriateamount of gas to be admitted to the hot-blast stove. The air isintroduced by means of a mover, preferably a centrifuge such as a bloweror the like, with the quantity moved determined by means of a ratiocontroller. In operation, the intake of air is inevitably interruptedwhen the mover breaks down-due to the fracture of the clutch, forinstance, or to current failure. The hot-blast stove then only receivesgas, and this may result in serious explosions.

The invention aims to overcome this drawback. It makes provision fordisruptions in air intake by interposing a gas safety device consistingessentially of a safety stop valve that cuts off the gas supply ahead ofthe butterfly valve which regulates the admission of gas, said safetystop valve being operated in response to the pressure in the air feedduct and the electric line current.

The above and other objects, features and advantages of the presentinvention will be more fully understood from the following descriptionconsidered in connection with the accompanying illustrative drawings.

In the drawings:

FIG. 1 is a schematic representation of a gas safety device inaccordance with the invention; and

FIG. 2 is a schematic drawing of part of the circuitry of FIG. 1, butarranged differently from FIG. 1 for purposes of explanation.

Referring now to the drawings and specifically to FIG. 1, there is showna hot blast stove HBS which is adapted to be heated so that it maysubsequently have air passed therethrough in order to supply hot blastto a blast furnace. The hot blast stove HBS is provided with a burnershut-off valve BV and a gas shut-off valve GV. The gas and the air whichform the gas air mixture to be burned in the combustion chamber are fedseparately to the hot blast stove through the burner. The burner shutoffvalve BV controls both the passage of the air and the gas supply. Thegas is fed through a gas main GM and the air is fed through the air mainAM by means of a fan 1. In the gas main GM there is provided a gasregulating butterfly valve GRBV which controls the amount of gasfurnished to the burner. The gas regulating butterfiy valve GRBV isoperated by a push button switch 17 under control of the stoveattendant. The gas regulating butterfly valve is associated with aswitch SBVCS (safety butterfly valve control switch) having contacts 00which are automatically closed as soon as the push button switch foropening the gas regulating butterfly valve has been actuated.

In accordance with the invention, there is also provided a gas safetybutterfly valve in the gas main which is affected, for the purposes ofsafety, by the pressure of the air in the air main, as will behereinafter seen in greater detail. The gas safety butterfly valve isdirectly opened or closed under the direct control of a conventionalprime "ice mover such as a servo motor 11, operatively connected to theadjusting stem 14 of the gas safety butterfly valve GSBV. When motor 11is energized it is operative to open the gas safety butterfly valveGSBV, and when motor 11 is de-energized it is operative to close the gassafety butterfly valve GSBV. The full lines in FIG. 1 indicate thede-energized condition of motor 11 at which time valve GSBV is fullyclosed. The gas safety butterfly valve GBVS has associated therewith alimit switch SBVLS (safety butterfly valve limit switch) having contactsa-a which are closed when the gas safety butterfly valve GSBV is broughtto its fully opened position. The operation of motor 11 is directlycontrolled by a relay MR which has a plurality of sets of contactsassociated therewith, namely, contacts bb, c-c and d-d. When relay MR isenergized, all three sets of contacts controlled thereby are closedresulting in the energization of motor 11.

A signal lamp GSBV-5L is provided in series with contacts aa of switchSBVLS so that when said contacts are closed the signal lamp GSBVSLbecomes lit.

A pressure gage SBVPS having contacts e-e' is connected to air main AM.The contacts e--e in the pressure gage SBVPS are closed when thepressure in line AM falls below a predetermined value set therefor. Airmain AM is also provided with a conventional combustion air regulatingbutterfly valve ARBV, which is provided with a switch SBVIS havingcontacts ff'. Contacts fof switch SBVIS are open when valve ARBV isclosed and contacts f' are closed when valve ARBV is open.

A time delay relay SBVTR, interconnected with the other components asshown in FIG. 1, controls a set of contacts g-g'. When relay SBVTR isenergized it is operative to instantaneously close contacts g-g thereof,and these contacts remain closed for only an adjustable period of timeafter which they are open, for reasons which will be fully set forthhereafter. The time delay relay SBVTR is of conventional type; forexample, a bimetal thermos-tat 18 completes the circuit through therelay coil and parallel with an electrical heater 19, so that after therelay is energized the heater starts warming the bimetal until, after apredetermined time, the bimetal will warp and open the relay circuitthereby de-energizing the relay. Another relay SBVAR, as shown in FIG.1, is interconnected with the other elements of the circuitry. RelaySBVAR controls a pair of sets of contacts namely, contacts h-h' andcontacts 'j'. When relay SBVAR is unenergized (the condition shown inFIG. 1), contacts hh thereof are open and contacts jj thereof areclosed. When relay SBVAR becomes energized, it is operative to closecontacts hh thereof and open contacts jj' thereof.

The hot blast stove HBS is provided with a combustion chamber walltemperature control instrument WTC, such as a pyrometer, which controlsa set of contacts k-k. The control instrument WTC is operative, underthe control of thermal element TH, kk' thereof closed at all times,except when the temperature of the combustion wall chamber drops below apredetermined temperature which is preferably set to be the ignitiontemperature of the gas. Contacts kk' of WTC are linked with the otherparts of the circuitry, as shown in FIG. 1.

A main distribution switch SBVDS having contacts l-l' and m-m' connectsthe circuitry of FIG. 1 to power lines R and O.

For purposes of explanation only, it is noted that when a hot blaststove is changed from the On Blast condition to the On Gas condition,all the valves of the stoves are operated in interlocked sequencestarting with the closing of the hot blast valve (not shown), closing ofthe cold blast valve (not shown), and opening of the chimney valve (notshown). After the chimney valve has been fully opened, the burnershut-off valve BV and the gas shut-off valve GV are opened. As soon asthe burner shut-off BV valve is fully opened, a circuit is completed tothe fan which becomes operative to force air into the air main AM. Anapparatus for automatically operating the valves and fan in suchinterlocked Sequence is fully disclosed in application Serial No.682,913, filed September 9, 1957, now Patent No. 2,931,635, of which Iam a co-inventor, which patent is also assigned to the assignee hereof.'Ihe interlocked sequence of operation of the valves set forth above isonly for purposes of explanation and does not form part of thisinvention. Similarly, the hot blast valve, cold blast valve and chimneyvalve are referred to only by way of background information and do notform part of this invention.

Before the full operation of the invention is explained, reference ismade to FIG. 2 which represents the identical circuitry as that shown inFIG. 1, but arranged differently for purposes of explanation. All thecontacts and components shown in FIG. 2 are shown in 'FIG. 1, and theirelectrical connections are identical to those shown in FIG. 1. In thisconnection, it will be noted that FIG. 1 shows the condition of thesystem after the gas shut-off valve GV has been opened but before thegas regulating butterfly valve GRBV has been opened by the attendant. Inthis condition of the system:

(1) Contacts o-' of switch SBVCS are open;

(2) Air regulating butterfly valve ARBV is closed and contacts f-f ofswitch SBVIS are open;

(3) The fan has begun to operate as a result of the opening of the gasshut-off valve and there is enough pressure in the air main AM (betweenARBV and the fan) to open contacts ee' of SBVPS;

(4) Relay MR is unenergized and contacts bb, c-c and dd' thereof areopen;

(5) Motor 11 is unenergized whereby the gas safety butterfly valve GSBVis closed and contacts aa' of limit switch SBVLS are open;

(6) Signal lamp GSBV-SL is unlit;

(7) Relay SBVTR is unenergized and contacts gg' thereof are open;

(8) Relay SBVAR is unenergized whereby contacts h-h' thereof are openand contacts jj thereof are closed; and

(9) It will be assumed that the wall temperature is above thepredetermined value set therefor, and contacts k-k of WTC are closed.

FIG. 2 represents the above components in exactly the same condition asin FIG. 1.

The operation of the invention will now be described.

After the gas shut-off valve has been fully opened as set forth above,the stove attendant opens the gas regulating butterfly valve GRBV as faras necessary to burn the required amount of gas in the burner. Aspreviously described, at the same instant that the gas regulatingbutterflyvalve GRBV is opened, contacts 00' of switch SBVCS are closed.Referring now to the circuitry in FIGS. 1 and 2, it will be noted thatthe closing of contacts 0-0 of switch SBVCS causes a circuit to becompleted from power line R through said contacts 00 of SBVCS, contactsk-k of WTC (provided the walls of the combustion chamber are at atemperature above the predetermined temperature set therefor), to line 0thereby energizing delay relay SBVTR. The energization of relay SBVTR isoperative to immediately close contacts g-g' thereof. As alreadyexplained above, the fan has been started due to the operation of theburner shut-off valve. As soon as the fan makes a certain number ofrevolutions, the pressure at the fan discharge will increase. With thepressure at the fan discharge above a certain adjustable pressure,contacts e-e' of SBVPS are open, and as shown in FIG. 2, the opencontacts e--e' of SBVPS cause relay SBVAR to be unenergized. Theunenergized condition of SBVAR causes contacts jj thereof Ito be closed.A circuit is now complete from line R through contacts 0--0 of SBVCS,contacts kk of WTC, contacts g-g of SBVTR, contacts jj' of SBVAR to line0, thereby energizing relay MR. It will be remembered that relay SBVTRis a delay relay and will remain energized only for an adjustable periodof time.

The energization of relay MR causes contacts bb, cc, and dd (FIG. 1) toclose and this immediately energizes motor 11 and causes the latter toopen the gas safety butterfly valve GSBV to its fully opened position,at which time contacts aa' of limit switch SBVLS are closed. As bestshown in FIG. 2, the closing of contacts aa of SBVLS completes a circuitthrough signal lamp GSBV-SL and the latter becomes lit to indicate thatthe gas safety butterfly valve is fully opened. So long as relay MRremains energized, the gas safety butterfly valve GSBV remains openunder the action of motor 11. With the gas safety butterfly valve GSBVin its fully opened position the gas can begin to flow through theburner and will be controlled by the position of the gas regulatingbutterfly valve GRBV. By means of a fuel-air ratio control (combustioncontrol), the combustion air butterfly valve ARBV is open to allow aflow of combustion air corresponding to the gas volume. The time whichis necessary for the combustion control to respond to the gas flow andto effect the operation of the combustion air butterfly valve ARBV isless than the time delay of delay relay SBVTR. As soon as the fuel-airratio control (combustion control) responds and opens the combustion airbutterfly valve ARBV, contacts f-f' of switch SBVIS are closed.Referring now specifically to FIG. 2, it will be noted that whencontacts f--- of SBVIS are closed, a circuit is complete to relay MRtherethrough, regardless of whether contacts gg' of relay SBVTR areopened or closed. In this way, when the time delay of relay SBVTR hasexpired, causing contacts gg' of SBVTR to open, the circuit to relay MRwill nevertheless remain energized by virtue of contacts f of SBVISwhich are closed. This will be true if the combustion air butterflyvalve ARBV has been opened. If, however, during the delay time of delayrelay SBVTR the combustion air butterfly valve ARBV has not been openedfor any reason whatsoever, then as soon as contacts gg' of relay SBVTRopen, after the time delay, there will be an open circuit to relay MR toimmediately de-energize the same and cause motor 11 to close the gassafety butterfly valve and thereby prevent any gas from entering intothe stove. It is of course obvious that if gas were permitted to enterthe stove without there also being air, there would result possibleexplosion and other dangers. Accordingly, it

' is seen that the electrical interconnection between the gas dition ofthe gas safety butterfly valve GSBV depends upon the energized conditionof motor 11, so that'as soon as the latter is dc-energized by virtue ofa power failure, the gas safety butterfly valve GSBV will immediately beclosed.

If, for any reason, Whether it is due to power failure or other reason,the fan ceases to operate to thereby stop the flow of combustion airinto the stove, there results an automatic closure of the gas safetybutterfly valve GSBV. More specifically, if the fan ceases to operate,the pressure within air main AM will fall below the predetermined valueset for switch SBVPS, so as to cause contacts e-e' thereof to close. Asbest seen in FIG. 2, the closure of contacts ee' of switch SBVPScompletes a circuit which energizes relay SBVAR. The energization ofrelay SBVAR immediately closes contacts h-h thereof to thereby completea holding circuit for relay SBVAR, and the energization of relay SBVARalso immediately opens contacts jj thereof to immediately interrupt thecircuit to relay MR and thereby immediately cause the de-energization ofmotor 11 and the closing of gas safety butterfly valve GSBV. Thus, it isseen that the present invention provides for the automatic closure ofthe gas safety butterfly v-alve GSBV in response to the failure tomaintain the desired air pressure in the air main AM, for whateverreason.

In the event that the gas safety butterfly valve GSBV has been closeddue to the drop of pressure in air main AM as described above, it willbe noted that relay SBVAR remains energized through contacts hh'thereof. Also, so long as relay SBVAR remains energized, contacts jjthereof will be open to prevent the gas safety butterfly valve frombeing reopened even if the pressure inside the air main is subsequentlyrestored to cause contacts e-e of switch SBVPS to open. Accordingly, ifit is desired to open the gas safety butterfly valve again, it isnecessary, after the system has been placed back in order, to first openthe contacts -0 of switch SBVCS in order to de-energize relay SBVAR.This is done by first closing the gas regulating butterfly valvecompletely, and in this way, open contacts 0-0' of SBVCS. Thisde-energizes rel ay SBVAR as well as the rest of the system. With relaySBVAR in the de-energized condition, contacts hh' thereof are open andcontacts jj thereof are closed. It is now possible to once again startthe operation of the system by opening the gas regulating butterflyvalve GSBV in the manner explained above.

According to the invention, there also results a safety device for thehot blast stove when the latter is changed from the On Gas condition toanother condition, such as the On Bottled or On Blast condition. Morespecifically, when a stove is about to be changed from the On Gascondition to another condition, it is customary for the stove attendantto reduce the gas flow by closing the gas regulating butterfly valveGRBV, before the operator actually changes the condition of the stovefrom On Gas to On Blast. That means that the gas regulating butterflyvalve is normally closed before the change-over of the stove begins.With the closing of the gas regulating butterfly valve the combustionbutterfly valve is also closed through the previously mentionedcombustion control. When the combustion air regulating butterfly valveis so closed, contacts f of switch SBVIS are opened andthisautomatically causes the de-energization of motor 11 and the closure ofthe gas safety butterfly valve GSBV. In this way, the gas safetybutterfly valve becomes closed prior to the changeover operation.

Thus it is seen that, in accordance with the present invention, severalobjectives are accomplished. More specifically, it will be seen that theinvention prevents the flow of gas to the burner in case the combustionwall temperature is below a certain predetermined value, which ispreferably set at the temperature at which the gas-air mixture willignite. This prevents possibilities of having an unburned gas and airmixture enter the combustion chamber and possibly causing an explosiontherein. The invention also prevents the gas flow in the event of apower failure and in the event that the fan fails to supply air which isnecessary for a satisfactory combustion.

While I have shown and described the preferred embodiment of myinvention, it will be understood that the invention may be embodiedotherwise than as herein specifically illustrated or described, and thatin the illustrated embodiment certain changes in the details of 6construction and in the form and arrangement of parts may be madewithout departing from the underlying idea or principles of thisinvention within the scope of the appended claims.

I claim:

1. In a hot blast stove adapted to be heated and supply hot blast to ablast furnace, gas conduit means for introducing gas into said stove,air conduit means for introducing air into said stove, valve means insaid gas conduit means for regulating the amount of gas introduced intosaid stove, valve means in said air conduit for regulating the amount ofair introduced into said stove, gas safety valve means operative whenclosed to prevent any gas from being introduced into said stove, meansfor opening said gas safety valve means, said opening means for said gassafety valve means being operative to open the latter only after saidgas regulating valve means has 7 been opened, and means operative toclose said gas safety valve means in response to the failure of said airregulating valve means to open a predetermined period of time after saidgas safety valve means has been opened.

2. In a hot blast stove adapted to be heated and supply hot blast to ablast furnace, gas conduit means for introducing gas into said stove,air conduit means for introducing air into said stove, valve means insaid gas conduit means for regulating the amount of gas introduced intosaid stove, valve means in said air conduit for regulating the amount ofair introduced into said stove, gas safety valve means operative whenclosed to prevent any gas from being introduced into said stove, meansfor opening said gas safety valve means, said opening means for said gassafety valve means being operative to open the latter only after saidgas regulating valve means has been opened, means for preventing saidopening means from being operative unless the combustion chambertemperature of said stove is above a predetermined value, and meansoperative to close said gas safety valve means in response to thefailure of said air regulating valve means to open a predeterminedperiod of time after said gas safety valve means has been opened.

3. In a hot blast stove adapted to be heated and supply hot blast to ablast furnace, gas conduit means for introducing gas into said stove,air conduit means for introducing air into said stove, valve means insaid gas conduit means for regulating the amount of gas introduced intosaid stove, valve means in said air conduit for regulating the amount ofair introduced into said stove, gas safety valve means operative whenclosed to prevent any gas from being introduced into said stove, meansfor opening said gas safety valve means, said opening means for said gassafety valve means being operative to open the latter only after saidgas regulating valve means has been opened, and means operative to closesaid gas safety valve means in response to the failure of said airregulating valve means to open a predetermined period of time after saidgas safety valve means has been opened, and additional means forautomatically closing said gas safety valve means when pressure in saidair conduit falls below a predetermined value.

4. In a hot blast stove adapted to be heated and supply hot blast to ablast furnace, gas conduit means for introducing gas into said stove,air conduit means for introducing air into said stove, valve means insaid gas conduit means for regulating the amount of gas introduced intosaid stove, valve means in said air conduit for regulating the amount ofair introduced into said stove, gas safety valve means operative whenclosed to prevent any gas from being introduced into said stove, meansfor opening said gas safety valve means, said opening means for said gassafety valve means being operative to open the latter only after saidgas regulating valve means has been opened, means for preventing saidopening means from being operative unless the combustion chambertemperature of said stove is above a predetermined value, and meansoperative to close said gas safety valve means in response to thefailure of said air regulating valve means to open a predeterminedperiod of time after said gas safety valve means has been opened, saidlast mentioned means including a time delay relay which is energizedupon the opening of the gas regulating valve and which remains energizedfor said predetermined period of time and a switch which is closed inresponse to the opening of said air regulating Valve means, andadditional means for automatically closing said gas safety valve meanswhen the pressure in said air conduit falls below 10 a predeterminedvalue.

References Cited in the file of this patent UNITED STATES PATENTSWheeler Apr. 24, Bargeboer June 14, Ashcraft Nov. 30, Riehl June 16,Hudson Feb. 11, Arant Dec. 8,

FOREIGN PATENTS Germany Dec. 12,

